Such metal cutting tips have long been proposed and used, whether the metal cutting tip constitutes an integral part of the metal cutting tool or whether the metal cutting tip forms part of a replaceable cutting insert which is releasably held, for example by screw clamping or by wedge clamping, in an appropriate tool holder. Examples of such metal cutting inserts having circular cutting edges are described in U.S. Pat. Nos. 4,626,140; 4,844,668; 4,946,319 and published European Patent Application No. 300172.
Such cutting tips having circular cutting edges are generally employed in turning operations where the cutting tip is designed to machine a workpiece into a relatively complicated cross-sectional shape, thereby requiring the relative motion of the cutting tip with respect to the workpiece in a continuously curving direction. It will be appreciated that, as a consequence, the extent of contact between the circular cutting edge and the workpiece, as well as the direction of contact (i.e. the angle between a normal to a tangent at the region of contact and the longitudinal axis of the cutting tool) vary with the relative displacement of the cutting tool with respect to the workpiece.
These continuous changes, both in the extent and direction of contact, which are inherent in the use of the circular cutting edge for the purposes indicated, make it increasingly difficult to control the formation and disposal of the chips generated during the turning operation.
Thus, it is known that chips generated with such cutting tips are generally thinner than those generated with cutting tips having a straight cutting edge when the cutting operation takes place under identical conditions of cutting depth and feed rate. Furthermore, it is known that the cross-sectional area of the chips so generated vary in accordance with the extent and direction of contact between the cutting edge and the workpiece. As a consequence of the general thin nature of the chips and their non-uniform cross-sectional area, it has been found very difficult to control the direction of flow of the chips and, in consequence, the provision of effective chip forming and breaking means is rendered more difficult. Thus, as will be readily appreciated, thin chips tend to bend easily and are therefore not readily broken. The provision of conventional means to break the chip and the requirement that these means be available for chips generated in varying directions, carry with it the introduction of an increased resistance to chip flow. This, in turn, leads to an increase in the forces which have to be expended during cutting and also gives rise to vibrations of the cutting system and to a consequent reduction in the surface quality of the machined workpiece.
Known metal cutting tips such as those, for example, described in the prior art referred to above, have not adequately dealt with this problem.
It is therefore an object of the present invention to provide a new and improved cutting tip having a circular cutting edge, in which the above-referred-to problems involved in the formation and disposal of the cutting chips, are significantly reduced.